1. Field of the Invention
This invention relates to a small-sized hydroelectric generator for generating electricity by utilizing the water flow that runs inside a water pipe.
2. Description of the Prior Art
A conventional small-sized hydroelectric generator is known, in which electricity is generated by utilizing water flowing inside a water pipe for use as a source of electricity for controlling a valve of automatic hand washer or the other devices, or as a source of electricity for products using a dry battery, for example, by charging up a condenser or an accumulator.
A structure of the conventional small-sized hydroelectric generator is as follows. Namely, an inflow port connecting and communicating with the water pipe is formed at an end of a casing and an outflow port is formed on the other end thereof. An electricity generating section comprising a stator and a rotator is arranged inside the casing. An impeller is integrally mounted to the rotator so that the impeller may be rotated by the water flow coming from the inflow port. Thus the rotator is rotated to make the stator generate an induced voltage and electricity, while the water that is used to rotate the impeller is made to drain to the outflow port through a passage formed to go through the center part of the rotator. (See Patent Publication 2000-213446, for example.)
Patent Document 1:
Japanese Patent Publication 2000-213446
However, according to the conventional small-sized hydroelectric generator as mentioned above, since a whole quantity of water flowing inside the water pipe is applied to the impeller for use as a rotational energy for the rotator, the output voltage from the stator increases in proportion to the quantity of water flow, as shown in FIG. 4, whereby not only a constant and stable voltage may not be obtained but also the impeller and a shaft bearing which supports a medial axis of rotation of the rotator may be worn out for a short period of time when the generator is connected to the water pipe having much quantity of flow or having a high water pressure, because the impeller rotates at a higher speed than a necessity requires.